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progress of the reaction was monitored by using TLC
and GC–MS. After the completion of the reaction, the
mixture was cooled to 258C and CH Cl and H O were
2
2
2
added to it. The layers were separated, and the aqueous
phase was extracted with CH Cl . The combined organic
2
2
extracts were washed with brine, dried over Na SO , and
2
4
concentrated under reduced pressure. The residue was
subjected to silica gel column chromatography
CH Cl /hexane=1:3) to afford acetophenone (2a) in
a
(
2
2
9
0% yield (54.1 mg) (Table 2, entry 1).
A representative method for the one-pot trans-
formation of alkynes into chiral alcohols: Phenyl-
acetylene (1a)
Scheme 1. Possible reaction pathway for the Co-catalyzed hydration of alkynes.
The 10 mL Schlenk tube was charged with phenylacety-
lene (0.5 mmol, 51 mg), methanol (0.625 mL), the catalyst
Conclusions
(
2 mol%), and then H SO4 (10 mmol, 2.0 mol%) dissolved in H O
2
2
3
+
(2.2 mmol, 0.04 mL) was added. The mixture was heated at 808C
for 20 h under air in a closed tube with a magnetic stir bar. After
the tube was cooled to 258C, the resulting mixture was bubbled
We have demonstrated the salen–Co -catalyzed hydration of
terminal alkynes to methyl ketones as well as the one-pot
transformation of alkynes into chiral alcohols by the combina-
tion of hydration and transfer hydrogenation catalysts. We be-
with argon for 15 min. Then, [RuCl (p-cymene)]2 (0.5 mol%) and
2
TsDPEN (1 mol%) were added to the mixture. The tube was then
3
+
[15]
lieve that the use of easily available salen–Co complexes as
catalysts makes this hydration of terminal alkynes practical.
Further studies to clearly understand the reaction mechanism
and the synthetic applications are ongoing in our laboratory.
sealed, and the mixture was stirred at 608C for 1 h. After the
tube was cooled to RT, a formic acid–triethylamine azeotropic mix-
ture (5:2, 0.3 mL) was added and the mixture was stirred at RT for
2
0 h. The progress of the reaction was monitored by using TLC
and GC–MS. After the completion of the reaction, CH Cl and H O
2
2
2
were added to the mixture. The layers were separated, and the
aqueous phase was extracted with CH Cl . The combined organic
Experimental Section
2
2
extracts were washed with brine, dried over Na SO , and concen-
2
4
General information
trated under reduced pressure. The residue was subjected to
a silica gel column chromatography (CH Cl /hexane=1:3) to afford
2
2
The GC–MS spectra were recorded on an Agilent Technologies
1
-phenylethanol (3a) in 92% yield (56.1 mg) (Table 3, entry 1).
1
13
7
890A/5975C system. The H and C NMR spectra were recorded
on a Bruker Avance III 400 MHz NMR spectrometer. The GC analysis
was performed on an Agilent Technologies 6820 (SE-54, 50 mꢁ
(
R)-1-Phenylethanol (3a)
0
.25 mmꢁ0.33 mm) system equipped with a flame ionization de-
tector. The ee values were determined by GC analysis on an Agilent
820 system equipped with a Supelco BETA DEX 120 capillary
1
H NMR (400 MHz, CDCl ): d=1.47 (d, J=6.4 Hz, 3H), 2.13 (br, 1H),
3
1
3
6
4.86 (q, 1H), 7.24–7.28 (m, 1H), 7.31–7.36 ppm (m, 3H); C NMR
column or from HPLC analysis on a Waters-Breeze system (2487
Dual l Absorbance Detector and 1525 Binary HPLC Pump). Chiral-
pak OD-H columns were purchased from Daicel Chemical Indus-
tries, Ltd.
(100 MHz, CDCl ): d=25.2, 70.4, 125.4, 127.5, 128.5, 145.9 ppm.
3
(R)-1-(4-Methylphenyl)ethanol (3b)
Phenylacetylene derivatives and other commercially available
chemicals were obtained from Alfa Aesar or Aldrich Chemical and
used as received without pretreatment unless otherwise stated.
1
H NMR (400 MHz, CDCl ): d=1.47 (d, J=6.4 Hz, 3H), 1.92 (br, 1H),
3
2
.35 (s, 3H), 4.84 (q, 1H), 7.15 (d, J=8.0 Hz, 2H), 7.25 ppm (d, J=
13
3
+
8.0 Hz, 2H); C NMR (100 MHz, CDCl
128.4, 129.2, 137.2, 142.9 ppm.
): d=21.1, 25.1, 125.4, 129.2,
3
Salen ligands and salen–Co –OAc complexes C1 and C2 were pre-
[14f,16]
[15]
pared according to the reported methods.
TsDPEN, 4-ethy-
nylbiphenyl, 4-ethynyl-1,2-dimethoxybenzene, and 1-ethynylnaph-
[17]
thalene
were prepared according to the literature methods.
(
R)-1-(3-Methylphenyl)ethanol (3c)
Column chromatography was generally performed on silica gel
plates (200–300 mesh), and TLC inspections were performed on
silica gel GF254 plates.
1
H NMR (400 MHz, CDCl ): d=1.45 (d, J=6.4 Hz, 3H), 2.23 (br, 1H),
3
2
7
7
.34 (s, 3H), 4.80 (q, 1H), 7.06–7.08 (m, 1H), 7.12–7.16 (m, 2H),
13
.20–7.24 ppm (m, 1H); C NMR (100 MHz, CDCl ): d=21.4, 25.1,
3
0.3, 122.4, 126.1, 128.1, 128.4, 138.1, 145.8 ppm.
A representative method for the hydration of terminal al-
kynes: Phenylacetylene (1a)
(
R)-1-(2-Methylphenyl)ethanol (3d)
The 10 mL Schlenk tube was charged with phenylacetylene
1
(
(
(
0.5 mmol, 51 mg), methanol (0.625 mL), and the catalyst
H NMR (400 MHz, CDCl ): d=1.45 (d, J=6.4 Hz, 3H), 1.80–2.00 (br,
3
2.0 mol%), and then H SO (10 mmol, 2.0 mol%) dissolved in H O
1H), 2.33 (s, 3H), 5.10 (q, 1H), 7.11–7.24 (m, 3H), 7.49–7.51 ppm
(m, 1H); C NMR (100 MHz, CDCl ): d=18.9, 23.9, 66.8, 124.5,
2
4
2
13
2.2 mmol, 0.04 mL) was added. The mixture was heated at 808C
3
for 20 h under air in a closed tube with a magnetic stir bar. The
126.4, 127.2, 130.4, 134.2, 143.9 ppm.
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ChemCatChem 2014, 6, 1612 – 1616 1615